<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button>按钮</button>
    <p>123</p>
    <!-- 点击按钮即改变p文字 -->
    <script>
        var but = document.querySelector('button');
        var pp = document.querySelector('p');
        but.onclick = function() {
            var date = new Date();
            pp.innerText = date;
        }
    </script>
    <!-- 直接改变p文字 -->
</body>

</html>